LOS ANGELES/NEW YORK, Nov 4: “Ender’s Game,” the futuristic story of children forced to fight an enemy race, battled to the top of box office charts in the United States and Canada, defeating senior citizen buddy comedy “Last Vegas” and animated turkey tale “Free Birds.” Based on a best-selling 1985 novel, “Ender’s Game” collected $28 million in ticket sales over its first three days, according to studio estimates released on Sunday. (agencies)